1. Field of the Invention
The present invention relates to a field emission display (FED) and, more particularly, to a carbon nanotube field emission display (CNT-FED).
2. Description of the Related Art
Filed emission display (FED), having competitiveness in the panel display market, is a high-voltage display with a triode structure consisting of anode, cathode and gate electrode to achieve high illumination by applying a high voltage and a low current. FED has advantages of light weight and thin profile, like liquid crystal display (LCD), and advantages of high brightness and self luminescence, like cathode ray tube (CRT). In conventional FED processing, fluorescent material is formed on an anode substrate, an electron-emitting source with a discharge tip is formed on a cathode substrate, and a gate electrode is formed to surround the discharge tip. Thus, applying a high electric field generated from the gate electrode, electrons are released from the discharge tip and then the electrons are accelerated by applied high voltage to strike the fluorescent material, resulting in emitted cathode fluorescence. With regard to the fabrication of the electron-emitting source, molybdenum (Mo) metal is employed to form a micro-tip shape, despite attendant problems of complex process, expensive equipment cost and low throughput.
Recently, carbon nanotube (CNT) materials, having high mechanical strength and great electrical performance, have been used to form the electron-emitting source of FED. Since simple and low cost technologies, such as screen printing, chemical vapor deposition (CVD) and coating, are applied to coat/grow carbon nanotubes within an electron-emitting area, the product, CNT-FED, has high throughput and may be formed as a large-size display. FIG. 1 is a sectional diagram showing a primitive CNT-FED 10. The CNT-FED 10 has a cathode substrate 12, an anode substrate 14 over and parallel to the cathode substrate 12, a spacer 16 disposed in the vacuum space between the two substrates 12 and 14 for maintaining a predetermined vertical distance and resisting atmosphere pressure. The anode substrate 14 has a glass substrate 18, a plurality of fluorescent layers 20 patterned on predetermined regions of the glass substrate 18, and planarized Al film 22 formed on the exposed regions of the glass substrate 18. The first purpose of the Al film 22 is to serve as a conductive layer of the anode substrate 14, the second purpose is to serve as a reflective layer of the fluorescent layer 20, and the third purpose is to serve as a protective layer for protecting the fluorescent layer 20 from ion bombardment and electric-filed attraction. The cathode substrate 12 has a glass substrate 24, a plurality of cathode layers 26 patterned on predetermined regions of the glass substrate 24, a plurality of CNT structures 34 grown on each electron-emitting area of the cathode layer 26, an insulating layer 28 formed on peripheral region of the glass substrate 24, and a net-shaped metal layer 32 glued on the insulating layer 28 by frit. In addition, each opening 32a of the net-shaped metal layer 32 corresponds to each electron-emitting area of the cathode layer 26, thus the metal material of the net-shaped metal layer 32 surrounding the cathode layer 26 serves as a gate electrode 32b. 
However, the CNT-FED 10 has disadvantages. First, edge effect is found at the outer carbon nanotubes that surround the electron-emitting area, thus each fluorescent layer 20 emits a comparatively brighter light at periphery and a comparatively darker light at the center. This causes non-uniform luminescence and decreases luminescent property of the CNT-FED 10. Second, since only the edge of the net-shaped metal layer 32 is glued to the insulating layer 28 that is formed on the peripheral region of the cathode substrate 12, most of the gate electrodes 32b are suspended over the cathode substrate 12. As the size of the net-shaped metal layer 32 is increased, the center area of the net-shaped metal layer 32 easily droops and become uneven. This causes electrons to bombard the gate electrode 32 and forms non-uniform electric fields, which may vibrate the gate electrode 32 or even peel the net-shaped metal layer 32. Third, when removing organic materials at high temperature, preferably at 450xcx9c500xc2x0 C., part of the Al film 22 may be oxidized to become aluminum oxide, resulting in a decreased conductivity of the Al film 22. This leads to an accumulation of charges when electrons are emitted to bombard the anode substrate 14. Also, when the charges are accumulated to reach a critical amount, an arc phenomenon is formed in order to deplete the accumulated charges, and thus the brightness on the anode substrate 14 is burned out. Moreover, the accumulated charges may generate a repellent electric field that makes the subsequently emitted electrons unable to bombard the anode substrate 14. This decreases the electron quantities that bombard the anode substrate 14 and degrades the brightness that is emitted from the fluorescent layer 20. Fourth, no matter whether the electron-emitting source employs a metal tip or the CNT structure 34, a divergent phenomenon of the electrons is always found to cause cross-talk on the anode substrate 14. Furthermore, as the amount of emitted electrons is greater, the excessive electrons directly bombard the anode substrate 14 to generate a spark. Thus, a novel structure of the CNT-FED and an improved process of forming the same to solve the aforementioned problems are called for.
The present invention provides a CNT-FED with a novel cathode substrate and a novel anode substrate to solve the problems caused by prior art.
The carbon nanotube (CNT) field emission display has a cathode substrate having a cathode layer patterned on a glass substrate. The surface of the cathode layer is defined as a plurality of electron-emitting areas apart from each other, and a plurality of CNT structures is grown on the plurality of electron-emitting areas respectively.
A method of forming a cathode substrate comprises: providing a glass substrate on which a plurality of cathode layers are patterned; forming a plurality of ribs in each space between adjacent cathode layers, wherein the rib protrudes from the top of the cathode layer to reach a predetermined height; printing to form a net-shaped gate electrode layer on the plurality of ribs; and performing high-temperature baking.
The CNT-FED has an anode substrate with a plurality of fluorescent layers patterned on a glass substrate. A planarized Al film covers the fluorescent layers, and a metal sheet covers the Al film. The metal sheet has a plurality of openings, wherein the openings are corresponding to the fluorescent layers respectively.
The CNT-FED has a cathode substrate with a plurality of cathode layers patterned on a glass substrate, wherein each cathode layer has an electron-emitting area on which a CNT structure is formed. A plurality of ribs fills each space between adjacent cathode layers and each rib protrudes from the top of the cathode layer to reach a predetermined height. A net-shaped gate electrode layer is formed on the plurality of ribs, and a metal cap covers the gate electrode layer. The metal cap has a plurality of apertures, wherein the plurality of apertures is corresponding to the electron-emitting areas respectively.
Accordingly, it is a principle object of the invention to provide the metal sheet to prevent arc phenomenon.
It is another object of the invention to protect the gate electrode layer from vibrating and peeling.
Yet another object of the invention is to increase the luminescent uniformity and luminescent efficiency of the CNT-FED.
It is a further object of the invention to provide the metal cap to avoid cross-talk on the anode substrate.
Still another object of the invention is to provide the apertures on the metal cap to limit the emitting space of the direct-emitting electrons; thereby decreasing the amount of accumulated electrons is decreased to eliminate arcing.
These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings.